Optical microcavity resonator system

ABSTRACT

An optical resonator system includes a substrate, and a SPARROW optical waveguide disposed on the substrate for evanescently coupling light into an optical microcavity. The SPARROW waveguide includes a multi-layer dielectric stack formed of alternating high and low refractive index dielectric layers, and a waveguide core disposed on the dielectric stack. The waveguide core has an input end and an output end, and is adapted for transmitting optical radiation incident on the input end to the output end. The optical microcavity is disposed at a distance from the optical waveguide that is sufficiently small so as to allow evanescent coupling of light from the optical waveguide into the optical microcavity. The dielectric stack in the SPARROW waveguide isolates the waveguide core and the microcavity from the substrate, so that an optical coupling efficiency approaching 100% can be obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable

REFERENCE TO MICROFICHE APPENDIX

[0003] Not Applicable

FIELD OF THE INVENTION

[0004] The present invention relates to optical microcavity resonators,and in particular to highly efficient, low-loss optical microcavityresonators having relatively high quality factors (Q's).

BACKGROUND OF THE INVENTION

[0005] During the past few years, a substantial amount of research hasbeen performed in the field of optical microcavity physics, in order todevelop high cavity-Q optical microcavity resonators. In general,resonant cavities that can store and recirculate electromagnetic energyat optical frequencies have many useful applications, includinghigh-precision spectroscopy, signal processing, sensing, and filtering.Many difficulties present themselves when conventional planartechnology, i.e. etching, is used in order to fabricate high qualityoptical resonators, because the surfaces must show deviations of lessthan about a few nanometers. Optical microsphere resonators, on theother hand, can have quality factors that are several orders ofmagnitude better than typical surface etched resonators, because thesemicrocavities can be shaped by natural surface tension forces during aliquid state fabrication. The result is a clean, smooth silica surfacewith low optical loss and negligible scattering. These microcavities areinexpensive, simple to fabricate, and are compatible with integratedoptics.

[0006] Optical microcavity resonators have quality factors (Qs) that arehigher by several orders of magnitude, as compared to otherelectromagnetic devices. Measured Qs as large at 10¹⁰ have beenreported, whereas commercially available devices typically have Qsranging from about 10⁵ to about 10⁷. The high-Q resonances encounteredin these microcavities are due to optical whispering-gallery-modes (WGM)that are supported within the microcavities.

[0007] As a result of their small size and high cavity Q, interest hasrecently grown in potential applications of microcavities to fields suchas electro-optics, microlaser development, measurement science, andspectroscopy. By making use of these high Q values, microsphericcavities have the potential to provide unprecedented performance innumerous applications. For example, these microspheric cavities may beuseful in applications that call for ultra-narrow linewidths, longenergy decay times, large energy densities, and fine sensing ofenvironmental changes, to cite just a few examples.

[0008] In order for the potential of microcavity-based devices to berealized, it is necessary to couple light selectively and efficientlyinto the microspheres. Since the ultra-high Q values of microcavitiesare the result of energy that is tightly bound inside the cavity,optical energy must be coupled in and out of the high Q cavities,without negatively affecting the Q. Further, the stable integration ofthe microcavities with the input and output light coupling media shouldbe achieved. Also, controlling the excitation of resonant modes withinthese microcavities is necessary for proper device performance, butpresents a challenge for conventional waveguides.

[0009] In general, the desirable characteristics of a microcavitycoupler include: 1) efficient WMG excitation; 2) easy alignment of themicrocavity with respect to a coupler; 3) clearly defined ports; 4) arobust and integrable structure; and 5) a consistent and inexpensivefabrication process. One of the most efficient prior art methodsincorporates phase-matched evanescent wave coupling. One commonly usedapproach for phase-matched evanescent wave coupling is to polish downthe cladding of an optical fiber, until the evanescent field is locallyexposed. Other techniques have been used in the prior art for couplinglight into the microspheres, for example the prism coupler, and thetapered fiber coupler. For the tapered coupler, a tapered fiber isformed, i.e. a narrow waist is formed on a fiber by heating and gradualstretching.

[0010] While the above-mentioned techniques provide efficient coupling,these approaches suffer from a number of drawbacks. For example, mostcurrently existing techniques for the excitation ofwhispering-gallery-mode (WGM) resonances in optical microcavities arenot easily scalable for mass production. Also, the existing techniquesare not robust or versatile enough for desired measurement environments.The fabrication of both the exposed fiber and the tapered fiber isnontrivial and intricate, and the resulting couplers are rather fragile.In particular, the tapered fiber coupler requires delicately drawnfibers, less than 5 micrometers in diameter and suspended in air. Also,the prism coupler does not provide guided wave control. Further, theprism coupler uses bulk components, and is therefore less desirable forapplications that call for robustness.

[0011] Typically, good overall performance is gained by accessing theevanescent field in a waveguide. Also, only waveguide structures provideeasy alignment and discrete, clearly defined ports. Leakage from thesphere WGMs onto the fiber cladding modes lowers the couplingefficiency, however. High-Q microcavities are typically composed ofhigh-purity silica, a material whose low refractive index value iscommonly used for the cladding of planar fiberoptic waveguides. As aresult, a silica sphere coupled to a conventional surface waveguide willlose most of its energy to substrate and cladding radiation. This lossspoils the Q, and reduces the device efficiency. Because of cavity andwaveguide mode leakage into the substrate and into the modes within thefiber cladding, power extraction from the input optical radiation isinefficient.

[0012] There is a need for a robust and efficient system for couplinglight into high Q optical microcavities, so that the high Q values canbe fully utilized.

SUMMARY OF THE INVENTION

[0013] A method and system is presented for efficiently and robustlycoupling optical radiation into an optical microcavity resonator so asto excite resonance modes within the microcavity. In particular, high-Qoptical microspheric cavity resonators are evanescently coupled to anoptical waveguide chip that has a SPARROW (Stripline PedestalAnti-Resonant Reflective Optical Waveguide) structure. When thefrequency of the light propagating along the waveguide matches aresonant whispering gallery mode (WGM) of the microspheric cavity, lightis coupled into the microsphere. Coupling efficiencies of over 98% maybe attained.

[0014] The present invention features a low-loss, high-Q opticalresonator system. The optical resonator system includes a substrate, anoptical waveguide, and an optical microcavity, all integrated into asingle structure. The substrate is preferably substantially planar, andmay be made of silicon, by way of example. The optical waveguideincludes a multi-layer dielectric stack disposed on the substrate. Thedielectric stack includes alternating high and low refractive indexdielectric layers. A waveguide core is disposed on top of the dielectricstack. The waveguide core has an input end and an output end. Thewaveguide core is adapted for transmitting optical radiation incident onthe input end to the output end.

[0015] The optical microcavity is constructed and arranged so as tooptically interact with optical radiation propagating through theoptical waveguide. The optical microcavity may be a microdisk, amicrosphere, or a microring, by way of example. In one embodiment, theoptical microcavity may be fabricated by melting a tip of a silicaoptical fiber or wire. The optical microcavity may be substantiallyspherical in shape, and characterized by a diameter of about 50micrometers to about 500 micrometers.

[0016] Because of the alternating high- and low- index dielectriclayers, the reflectivity of the dielectric stack is very high. Inparticular, the reflectivity of the dielectric stack is high enough toisolate the optical modes in the microcavity and in the waveguide corefrom the substrate. The maximum distance between the optical microcavityand the optical waveguide is sufficiently small so as to allowevanescent coupling of light from the waveguide into the microcavity,namely the maximum distance is of the order of the wavelength of thelight incident upon the waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic diagram of the elements forming anintegrated optical system for coupling laser light onto an opticalmicrocavity resonator, constructed in accordance with the presentinvention.

[0018]FIG. 2 illustrates an optical microcavity resonator, constructedin accordance with the present invention.

[0019]FIG. 3A illustrates a SPARROW optical waveguide, constructed inaccordance with the present invention.

[0020]FIG. 3B illustrates a cross-sectional geometry of a SPARROWoptical waveguide.

[0021]FIG. 4 illustrates a numerically simulated field profile of aSPARROW optical mode.

[0022]FIG. 5A illustrates evanescent coupling of optical radiation froma SPARROW optical waveguide onto a WGM resonance mode supported within aring-shaped optical microcavity resonator.

[0023]FIG. 5B illustrates the intensity of the optical radiationtransmitted through the SPARROW waveguide illustrated in FIG. 5A whenthe input light wavelength is scanned across a WGM resonance.

[0024]FIG. 6 illustrates an integrated microcavity/waveguide structure.

[0025]FIG. 7 illustrates the waveguide transmission response of anoptical microcavity coupled to a SPARROW waveguide when the input lightwavelength is scanned across multiple WGM resonances.

DETAILED DESCRIPTION

[0026] The present invention provides a robust and efficientintegrated-optics system for coupling optical signals into microcavityresonators so as to excite, control and monitor the resonant modes inthe microcavity. In particular, the present invention features theevanescent coupling of laser light into optical microcavity resonators,using anti-resonant reflective optical waveguide structures.

[0027]FIG. 1 illustrates the elements forming an integrated opticalresonator system 10 for evanescently coupling light into an opticalmicrocavity, constructed in accordance with the present invention. Inoverview, the system 10 includes an optical microcavity 20, and awaveguide chip 30 that is used to couple light into and out of theoptical microcavity 20. In the illustrated embodiment, integration ofthe microcavity 20 and the waveguide chip 30 is accomplished using afiber stem 40, which remains attached to the optical microcavity 20,following the fabrication of the microsphere. An optical source 50,preferably a laser, provides a beam 60 of input radiation directed tothe waveguide. A photodetector 70 detects optical radiation transmittedthrough the waveguide 30.

[0028]FIG. 2 illustrates in more detail the optical microcavity 20,constructed in accordance with the present invention. Opticalmicrocavities are small spherical particles, disks, or rings, havingdimensions of the order of microns to millimeters. In the illustratedembodiment of the invention, the optical microcavity 10 is asubstantially spherical particle, typically made of silica. In apreferred embodiment, the optical microcavity 10 is fabricated bysurface tension shaping of the tip of freshly melted optical fiber.Melting of the tip of a silica wire or fiber may be accomplished througharcing in a fusion splicer, by means of a gas flame, or using ahigh-power laser (such as a CO₂ laser) to heat the glass. Microspheres,with diameters typically ranging from about 50 micrometers to about 500micrometers, are obtained by this method. In the illustrated embodiment,the optical microcavity 10 has a diameter of about 200 micrometers,although other sizes are also within the scope of the present invention.In a preferred embodiment, the fiber stem 40 may be left attached to themicrocavity, and used for maneuvering the microcavity relative to theoptical waveguide.

[0029] The most practical and versatile electro-optical couplingmechanisms which could be utilized for microcavity integration areplanar waveguide structures. As explained earlier, waveguide structuresprovide for easy alignment of the microcavity with respect to thecoupler, and discrete, clearly defined ports. Also, WGMs inmicrocavities can be efficiently excited using waveguides.

[0030] In particular, it is desirable to implement wafer-based, planaroptical waveguides, such as those used for integrated optics. Thesesolid, optical chip structures provide robustness and rigidity, alongwith the capability of integrated optical system to be fabricatedconsistently and inexpensively. Prior efforts at implementing a basicintegrated-optics coupler configuration using a microcavity and aconventional integrated-optics waveguide made of silica were frustrated,however, because of the difficulty of finding suitable cladding materialfor the integrated-optics waveguides. The silica waveguide would have tobe clad with a material having an index of refraction that is much lowerthan the index of refraction of silica, in order to avoid leakage ofincoming radiation into the cladding radiation modes. Materials havingan index of refraction much lower than the index of refraction of silicaare not readily available, however, so the above-described waveguidecoupling scheme was frustrated.

[0031] In the present invention, a SPARROW (stripline pedestalanti-resonant reflective optical waveguide) integrated-optics waveguideis implemented, in order to overcome the disadvantages mentioned above.FIG. 3A illustrates a SPARROW optical waveguide 110, constructed inaccordance with the present invention. The SPARROW waveguide 110provides an efficient and robust coupling mechanism for excitingwhispering-gallery-modes in an optical microcavity 102. The SPARROW 110includes a multi-layer, high-reflectivity dielectric stack 130 disposedon the substrate 120, and a waveguide core 140. The substrate 120 issubstantially planar, and in one embodiment is made of silicon.

[0032] The dielectric stack 130 is composed of alternating high (n_(H))and low (n_(L)) refractive index layers 131 and 132, made of adielectric material. As a result, the dielectric stack 130 functions asa high reflectivity dielectric mirror. The larger the number of layers131 and 132, the higher the reflectivity of the stack 130 becomes. Whilethe illustrated embodiment includes only one low index layer 132disposed between two high index layers 131, the number of the layers 131and 132 can be increased in order to increase the reflectivity of thestack 130. The alternating layers 131 and 132 forming the dielectricstack 130 provide a cladding for the SPARROW waveguide core 140, i.e.the layers forming the stack 130 may be regarded as cladding layers.

[0033] The high reflectivity of the dielectric stack 130 permitsisolation of the optical modes of the microcavity 102 and the waveguidecore 140 from the waveguide cladding and the substrate. By isolating thewaveguide core 140 using the high-reflectivity dielectric stack 130, theSPARROW 110 circumvents the need for obtaining low refractive indexcladding materials. As shown in FIG. 3A, one of the high refractiveindex layers 131 is in contact with the substrate 120.

[0034] In one embodiment, the high refractive index layer 131 is made ofSi (silicon), while the low refractive index layer 132 is made of SiO₂(silica). In one embodiment, the high refractive index n_(H) is about3.5, and the low refractive index n_(L) is about 1.45, although otherrefractive indices are also within the scope of the present invention.The refractive indices required for efficiently guiding light within thewaveguide depend on the wavelength of optical radiation.

[0035] The waveguide core 140 is disposed on top of the dielectric stack130, and is in contact with another one of the high refractive indexlayers 131. The waveguide core 140 includes an input end 142 and anoutput end 144, and is adapted for transmitting optical radiationincident on the input end 142 to the output end 144. In one embodiment,the waveguide core is made of silica, and is characterized by the lowrefractive index n_(L).

[0036]FIG. 3B illustrates a cross-sectional geometry of the SPARROWoptical waveguide 110. In FIG. 3B, the low refractive index layer 132 isshown as having a thickness d_(L) and a refractive index n_(L), and thehigh refractive index layer 131 is shown as having a thickness d_(H) anda refractive index d_(H). The waveguide core 140 in FIG. 3B is shown ashaving a thickness d and a width W, which are preferably selected toprovide an effective index N_(L) for the core 140 that is compatiblewith the excitation of resonance WGMs in the silica microcavity.

[0037] In a preferred embodiment, the thicknesses d_(L) and d_(H) of thelayers 131 and 132 are chosen to equal one quarter of the guided-lightwavelength. In an embodiment of the invention having a geometryillustrated in FIG. 3B, and with given values for n_(H), n_(L), and adesired operating wavelength λ_(O) (i.e., the wavelength that matches aWGM resonance within the optical microcavity), the values of d_(L) andd_(H) can be computed numerically so as to be equal to one fourth of theguided light wavelength. In one embodiment, the following values werechosen: high refractive index n_(H)=3.5; low refractive indexn_(L)=1.45; waveguide core width W=6.0 micrometers; waveguide corethickness d=2.0 micrometers; operating wavelength λ_(O)=1.55micrometers. For these values, the numerically computed effectiverefractive index n_(L) for the waveguide core is n_(L)=1.4026. In thisembodiment of the invention, the numerically computed thicknesses of thelayers 131 and 132 are: d_(L)=1.12 micrometers; d_(H)=120 nanometers.Other embodiments of the invention may have different values of n_(H),n_(L), d_(L), d_(H), W, and d.

[0038]FIG. 4 illustrates a numerically simulated field profile of aSPARROW optical mode. As seen from FIG. 4, the SPARROW optical modefield is essentially entirely contained within the waveguide core 140 ontop of the dielectric stack 130, and is isolated from the substrate 120.The successful elimination of both the sphere mode and the waveguidemode leakage into the substrate 120, as illustrated in FIG. 4, resultsin extremely high coupling efficiencies.

[0039]FIGS. 5A illustrates evanescent coupling of optical radiation fromthe SPARROW optical waveguide onto a WGM resonance 200 supported withina ring-shaped optical microcavity 102. An evanescent wave appearswhenever a light wave undergoes total internal reflection at adielectric interface, such as the interface between the silica waveguide140 and the surrounding air. As shown in FIG. 5A, the waveguide 140 hasa higher index of refraction, as compared to the surrounding air. Theevanescent portion of the waveguide mode field is the exponentiallydecaying portion of the waveguide mode field, outside the relativelyhigh index region of the waveguide. The evanescent wave decaysexponentially with the distance from the surface of the waveguide coreon a length scale of the order of the optical wavelength.

[0040] The coupling gap d between the microcavity 102 and the waveguide140 is selected to be within the range for evanescent coupling betweenthe waveguide 140 and the microcavity 102, i.e. of the order of onewavelength of the optical mode propagating in the waveguide. With thisconfiguration, evanescent coupling occurs between the waveguide 140 andthe microcavity 102 when the wavelength of the evanescent field of thewaveguide mode field matches the wavelength of a resonant WGM 200supported within the microcavity 102. In resonant WGMs, light is trappednear the surface of the microcavity by repeated total internalreflections, and travels in a circle around the microcavity near thesurface of the microcavity, as illustrated in FIG. 5A. The wavelengthsof the resonant WGMs are thus determined approximately by the radius rof the microcavity 102, i.e. WGM resonances occur at wavelengths givenby:

2πr=nλ.

[0041] When WGM resonances are excited in the microcavity 102, lightcontinues to circulate just inside the surface of the microcavity, withvirtually no loss except for residual absorption and scattering in thedielectric. This is why extremely high Q-factors, up to over 10¹⁰, canbe achieved in these dielectric microcavities. In practice, the shapeswhich are obtained for the optical microcavity 120 are not perfectlyspherical. As a consequence, many different radial and polar cavitymodes may be observed within the fine-tuning wavelength modulation cycleof the incident light. Each mode possesses a different linewidth andthus a different cavity Q.

[0042] The intensity of the light transmitted through the waveguide 140is detected by a photodetector 210 positioned at an output end 144 ofthe waveguide, as shown in FIG. 5A. The photodetector output isillustrated in FIG. 5B. When evanescent light just outside the surfaceof the waveguide 140 is coupled onto the microcavity 120 and a WGMresonance is excited within the microcavity, the intensity of theoptical radiation transmitted through the waveguide can approach zero atthe wavelength of the resonance, implying near 100% coupling efficiency,as shown in FIG. 5B. Because light at the resonance wavelength iscoupled into the microcavity resonator, a resonance dip 300 occurs inthe transmitted intensity. The cavity Q factor for the microcavity canbe determined by the linewidth of the resonance mode: the narrower thelinewidth, the higher the cavity Q. Linewidth is also affected by otherparameters such as surface quality, bending losses, and scatteringeffects, all of which contribute to the cavity Q.

[0043] A primary advantage of the SPARROW waveguide is that itfacilitates the integration of high-Q microsphere cavities ontowafer-based optical circuits. An integrated microcavity/waveguidestructure 400 is illustrated in FIG. 6. Bonding agents such as epoxy 410can be used to attach the fiber stem 420 to the waveguide chip 430. Thekey factors which determine the success of this integration techniqueare the system parameter sizes (fiber stem diameter and length, andmicrocavity diameter). When standard fiber (125 μm cladding diameter) isutilized as the fiber stem, there is sufficient stiffness to support anaverage-size microcavity (˜250 μm diameter). In the illustratedembodiment of the invention, a fiber stem 420 approximately 125 μm indiameter and a microcavity 440 approximately 200 μm in diameter areintegrated with a waveguide.

[0044] The SPARROW waveguide is characterized by a power extractionefficiency unmatched by any other prior art methods of coupling lightonto microcavity resonators, up to over 99%. FIG. 7 illustrates awaveguide transmission response of a microcavity coupled to a SPARROWwaveguide. The transmission spectrum is shown near a central resonancewavelength of about 1.55 um. Resonant dips can be observed in thespectrum as the microcavity extracts power from the waveguide. Thetransmitted power levels in the absence of the microcavity remain withinapproximately 5% of the peak values observed in FIG. 7. An extractionefficiency greater than 85% is seen from FIG. 7, however, extractionefficiencies over 98% have also been observed.

[0045] SPARROW couplers also provide the advantages that result fromlithographic fabrication. These advantages include the precise controlof component parameters, and the ease of large scale and/or batch modefabrication. The components of the SPARROW waveguide may be fabricatedusing: 1) thermal oxidation of a silicon wafer; 2) low-pressure chemicalvapor deposition; and 3) reactive ion etching. In one embodiment, thefabrication process for the SPARROW waveguide 110 is designed tominimize leakage loss at the operating wavelength of 1.55 μm. In thisembodiment, the fabrication process begins with 1.7 μm of thermaloxidation on a 4 inch wafer of silicon. This process is followed by a120 nm layer of amorphous silicon deposited at 560° C. by LPCVD (lowpressure chemical vapor deposition). Finally, 2.0 μm of silica is grownto form the core layer. The stack is then patterned by reactive-ionetching to form the SPARROW structure. The first 1-2 μm of etching maybe performed with a wet-etch step in order to generate smoother coresidewalls.

[0046] While the invention has been particularly shown and describedwith reference to specific preferred embodiments, it should beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims.

What is claimed is:
 1. An optical resonator system, comprising: A. asubstrate; B. an optical waveguide, comprising: (a) a multi-layerdielectric stack disposed on said substrate, said dielectric stackincluding alternating high and low refractive index dielectric layers;(b) a waveguide core disposed on said dielectric stack and having aninput end and an output end, said waveguide core being adapted fortransmitting optical radiation incident on said input end to said outputend, said waveguide core being in contact with one of said highrefractive index layers; and C. an optical microcavity constructed andarranged so as to optically interact with said optical radiationincident on said input end of said optical waveguide core.
 2. An opticalresonator system according to claim 1, wherein one of said lowrefractive index layers is in contact with said substrate, and one ofsaid high refractive index layers is in contact with said waveguidecore.
 3. An optical resonator system according to claim 1, wherein saidoptical microcavity is disposed at a distance from said opticalwaveguide that is sufficiently small so as to allow evanescent couplingbetween said microcavity and said optical waveguide.
 4. An opticalresonator system according to claim 1, wherein said optical microcavityhas a substantially spherical shape.
 5. An optical resonator systemaccording to claim 3, wherein said evanescent field is characterized byat least one frequency substantially equal to at least one resonant modeof said optical microcavity.
 6. An optical resonator system according toclaim 5, wherein at least one of said resonant modes of said opticalmicrocavity is a whispering gallery mode.
 7. An optical resonator systemaccording to claim 6, wherein said optical microcavity has asubstantially spherical shape, and wherein the wavelengths of thewhispering gallery modes of said microcavity are substantially equal torelated to λ, λ being related to the radius r and the degree ofsphericity of said substantially spherical microcavity by the formula:2πr=nλ, where n is a nonzero integer.
 8. An optical resonator systemaccording to claim 1, wherein said low index dielectric layer and saidwaveguide core comprises silica.
 9. An optical resonator systemaccording to claim 1, wherein said high index dielectric layer comprisessilicon.
 10. An optical resonator system according to claim 1, whereinsaid optical microcavity is selected from the group consisting ofmicrospheres, microdisks, and microrings.
 11. An optical resonatorsystem according to claim 1, further comprising an optical source forgenerating a beam of light directed to said input end of said opticalwaveguide.
 12. An optical resonator system according to claim 1, furthercomprising at least one detector constructed and arranged so as todetect output optical radiation from said output end of said opticalwaveguide.
 13. An optical resonator system according to claim 1, whereinsaid optical microcavity is made of silica.
 14. An optical resonatorsystem according to claim 1, wherein said optical waveguide forms anintegrated optical chip.
 15. An optical resonator system according toclaim 1, wherein said optical waveguide and said optical microcavityform an integrated optical chip.
 16. An optical resonator systemaccording to claim 1, wherein the coupling efficiency of said evanescentfield into said optical microcavity is from about 10% to about 99.99%.17. An optical resonator system according to claim 1, wherein thereflectivity of said dielectric stack is sufficient to isolate theoptical modes within said waveguide core from said substrate.
 18. Anoptical resonator system according to claim 1, wherein the reflectivityof said dielectric stack is sufficient to isolate the optical modes insaid microcavity from said substrate.
 19. An optical resonator systemaccording to claim 1, wherein said optical microcavity is fabricated bymelting one end of an optical fiber.
 20. An optical resonator systemaccording to claim 1, wherein said optical microcavity is characterizedby a quality factor (Q) from about 10⁵ to about 10¹⁰.
 21. An opticalresonator system according to claim 1, wherein said optical microcavityis characterized by a diameter of about 50 μm to about 500 μm.
 22. Anoptical resonator system according to claim 1, wherein said opticalmicrocavity is characterized by a diameter of about 200 μm.
 23. Anoptical resonator system according to claim 3, wherein said distance isless than one wavelength of said optical radiation propagating throughsaid optical waveguide.
 24. An optical resonator system according toclaim 1, wherein said high refractive index is about 3.5, and said lowrefractive index is about 1.45.
 25. An optical resonator systemaccording to claim 1, wherein the thickness and the width of saidwaveguide core is chosen so as to provide an effective refractive indexfor said waveguide core that matches the refractive index of saidmicrocavity when a resonant WGM is excited therewithin.
 26. An opticalresonator system according to claim 25, wherein said thickness of saidwaveguide core is chosen to match the wavelength of said opticalradiation propagating through said optical waveguide.
 27. An opticalresonator system according to claim 25, wherein said thickness of saidwaveguide core is about 2.0 μm, said width of said waveguide is about6.0 μm, and said effective refractive index for said waveguide core isabout 1.40.
 28. An optical resonator system according to claim 1,wherein the coupling efficiency of said evanescent field into saidoptical microcavity is about 99%.